Constant-flow irrigation tape and method of making

ABSTRACT

A constant-flow drip irrigation tape hose includes a primary flow path communicating water along the length of the hose. A secondary drip-flow path leads from the primary flow path to an emitter site outwardly of the hose. The hose is formed with a pair of variably spaced apart walls at least one of which is formed with a continuously-open channel defining part of the secondary flow path. A second variable-area part of the secondary flow path is defined by radial spacing of the pair of walls from one another. At least one of the pair of walls is responsive to internal water pressure in the primary flow path to open and close the variable-area part of the secondary flow path in response, respectively, to decreasing and increasing water pressure in the hose. A plurality of emitter sites are spaced regularly along a length of the hose. Consequently, the hose has at least one pressure range within which it provides a nearly constant drip-flow irrigation rate to plants of a row crop as the water pressure within the hose decreases over the length of an elongate run of hose.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to agricultural irrigation. Moreparticularly, the present invention relates to a tubular flexible hose,or tape, which is used to distribute water substantially uniformly atdiscreet locations spaced along its length. Such "tape" hoses arecreased longitudinally so that when they are not filled with water underpressure they collapse to a flat tape-like configuration. Such tapes aremore easily rolled, transported, and stored than are hoses which remainalways round in cross section. Consequently, the present inventionrelates to hose structure of the type generally recognized as "dripirrigation tape". Such drip irrigation tapes are widely used in row-cropfarming so that irrigation water is distributed to the soil immediatelyadjacent to the growing plants, and the entire field need not beirrigated. The use of such irrigation tapes results in considerablereduction in water use, loss of fertilizer, and accumulation of mineralsalts in arable agricultural soils.

2. Related Technology

A conventional hose for irrigation use is known in accord with U.S. Pat.No. 4,047,995, issued 13 Sep. 1977. This conventional irrigation hose ismade from an elongate strip of thin plastic film which is either foldedor wrapped sealingly on itself, or with a similar strip of plastic film,so that two layers of the plastic film are partially or fully overlappedand sealed together in facial contact. The strip or strips of plasticfilm form an elongate primary flow path along which a large-volume flowof irrigation water may pass. In order to provide plural small drip-likewater flows outwardly of the hose, the plastic film is not sealed toitself, or to the other strip of plastic film, in selected areas spacedalong the length of the hose. These areas define elongate tortuouspatterns communicating from the primary flow path outwardly of the hose.Consequently, when the hose is supplied internally with pressurizedwater, the areas where the plastic film is not sealed together separateslightly to form secondary drip flow paths and to allow water to seepbetween the layers of plastic film to plural spaced-apart fine-dimensionoutlets on the hose at which a dripping water flow may take place. Thatis, the areas where the plastic film is not sealed either to itself orto the similar strip of plastic film defines plural fine-dimensiontortuous, serpentine, or elongate and constricted secondary flow pathsspaced along the length of the hose and each leading from thelongitudinal primary water flow path outwardly to respectivespaced-apart outlet ports along the length of the hose.

With an irrigation hose according to the '995 patent, the rate ofdripping water flow from the outlets of the hose decreases along alength of the hose as the water pressure within the hose decreases. Thisdecrease in water pressure level in inescapable because of frictionresulting from the flow of the water, and the fact that water volume inthe hose decreases as the water is metered out through the drippingoutlets. The result is that irrigated plants near the water inlet end ofthe hose may receive an excess of water. Near the center of a run ofthis hose, the irrigated plants may receive the desired amount of water,and near the far end of the hose away from the water inlet, theirrigated plants will receive too little water.

Also, the size of the tortuous or serpentine passages through whichdripping water flow must escape the hose are so small that they areeasily clogged by debris and particulates in the hose. Moreover, thewater used for irrigation purposes may not be (and generally will notbe) potable water. Consequently, this water will frequently carrybacterial slime, algae, and particulates which can quickly plug thesmall metering passages of a hose like that taught by the '995 patent.Further, because these metering passages only really open when the hoseis pressurized, and are otherwise closed, once they become clogged theywill remain clogged. Relief of internal water pressure on this hose hasthe effect of allowing the drip passages to constrict and trap cloggingcontaminants in these passages. Further, the inlets to the tortuousmetering drip passages of this hose are disposed at a crevice or bitebetween the overlapped sheets of plastic film. Consequently, the primarywater flow is not particularly vigorous or turbulent as it passes theseinlets. Again, the result is a hose with drip outlets which clog easilyand which will not unclog. Finally, this hose provides outlet openingson the hose which allow reflux of environmental water and contaminationinto the metering passages. This reflux of water and contamination mayclog the dripping outlets. Also, small plant roots may find their wayinto the outlets on the hose, and again may clog the dripping outlets.

Another conventional drip irrigation hose which attempts to solve theproblem of inconsistent water outlet dripping flow rate along the lengthof a run of the hose is known in accord with U.S. Pat. No. 4,009,832,issued 1 Mar. 1977. The hose taught by the '832 patent the primary waterflow path is made by an elongate strip or strips of plastic film whichare partially or fully overlapped and sealed together to form a primarywater flow path. An inner flap or inner wall portion of the hosecooperates with an outer wall portion of the hose to define a throttlinggap. This structure results in a drip irrigation hose which is morenearly uniform in its rate of water delivery despite varying pressureover a length of the hose.

However, consideration of the structure for the drip irrigation hosesset forth in the '832 patent will reveal that this hose suffers frommany of the deficiencies described above with respect to the hose of the'995 patent. For example, even though the '832 patent asserts that thehose is self cleaning with respect to being able to flush outcontaminants (i.e., slime, algae, and particulates) because the flapportion of the inner wall will open up the metering or throttling gapwhen the hose is open for flushing, it is seen that the inlets from theprimary flow path of this hose to the secondary flow path and dripoutlets is still defined either at a crevice or bite along the length ofthe hose, or as simple holes perforating the inner wall perpendicularlyto the axis of the primary flow path. Primary water flow at these inletsto the secondary flow paths will be rather sluggish and contaminants caneasily enter these inlets. Further, flushing of the hose to removecontaminants clogging the secondary flow paths can have only a limitedeffect because the flap portion of the hose wall inherently must have aninitial contacting relationship with the overlying wall portion evenwhen the hose in not under pressure. Were the hose constructedotherwise, this flap portion would not form a pressure drop for themetered water flow and would not be urged into metering relationshipwith the outer wall of the hose. Consequently, this flap will not infact move out of engagement with the overlying wall portion of the hosesufficiently to release clogging contaminants.

Yet another conventional drip irrigation hose is known in accord withU.S. Pat. No. 4,247,051, issued 27 Jan. 1981. The drip irrigation hoseaccording to the '051 patent is formed similarly to the hoses discussedabove, with modifications directed to reducing clogging of the dripoutlets of the hose. More particularly, the size of the tortuous,serpentine, or elongate and restrictively small sized secondary flowpassages extending between the primary water flow path of the hose andthe drip outlets of the hose are increased so that it is not so easilyclogged by contaminants. However, the flow rate of water through thesecondary flow paths is controlled by the configuration of thesepathways so that water drip flow rates are maintained. The hose isformed with elongate ribs spacing the overlapped walls of the secondarymetering flow path away from one another. These ribs may be formed byadhesively securing a non-adhesive elongate spacer, such as amonofilament fishing line, between the overlapped walls of the hose.

An assertion for the hose provided by the '051 patent is that the inletand outlet holes of the secondary metering passages may be of sufficientsize as to not easily clog. Also, the water flow velocity in thesecondary metering passages is asserted to be sufficiently high thatself-cleaning of the inlet and outlet holes is provided. However, aclose consideration of the structure presented by the '051 patentsuggests that the objectives for this irrigation hose may not berealized in fact. Slotted intake opening to the secondary flow paths areprovided in one embodiment of this patent, with no particularexplanation of why these slotted openings would not themselves clog withcontaminants. A flexible flap type of outlet valve is provided also byan embodiment of this invention, which valve is configured so that itpresents a flow constriction and may not open wide in the event itbecomes partially clogged, so that the clogging material would beejected. The result is that the outlet valve could easily clog and theirrigation hose of the '051 patent includes features which defeat thepurpose of providing an irrigation hose with reduced clogging.

Still another conventional irrigation hose is known in accord with U.S.Pat. No. 4,722,759, issued 2 Feb. 1988. This irrigation hose provides alongitudinal primary flow path communicating with a longitudinalsecondary flow path via spaced apart inlets which are controlled by aninner flap portion of the overlapped walls of the hose to throttle waterflow responsive to the local pressure level of the water. At spacedapart drip outlets of this hose, the overlapped walls of the hose have arespective break in a longitudinal heat-sealed seam between theoverlapped walls. Consequently, the walls of the hose may separateslightly to allow water outflow at these outlets to the crops to beirrigated. Similarly to the irrigation hoses considered above, however,the hose of the '759 patent defines inlets to the secondary flow pathswhich are at a crevice or bite internally of the hose. Again, primarywater flow at these inlets could not be vigorous under normal irrigationuse conditions for the hose. Accordingly, frequent clogging of theseinlets to the secondary flow paths could be expected with this hose.

Additional conventional drip irrigation hoses or tapes are known inaccord with U.S. Pat. Nos. 4,548,360, issued 22 Oct. 1985; 5,118,042,issued 2 Jun. 1992; 5,192,027, issued 9 Mar. 1992; and 5,252,162, issued12 Oct. 1993, all of which are assigned to the assignee of the presentapplication.

In view of the interest in developing drip irrigation hoses whichprovide a more nearly constant irrigating water flow along a run of thehose despite the reduction in internal water flow pressure which occursalong a hose run, the California Agriculture Technology Institute hasprovided a formula by which the uniformity of water delivery may bemeasured. The Institute's publication No. 92100 sets out the formulaQ=K(H)^(x), where H is local primary water pressure (i.e., at the inletend of a drip-flow path of the hose leading to a water outlet), Q is therate of water flow from the drip-flow outlet of the hose, and K is aconstant. If "x" falls in the range from 0.5 to 1.0, the hose isconsidered not to be pressure compensated. That is, the delivery rate ofwater from the drip-flow outlets of the hose is simply a function of theinternal water pressure existing in the hose at particular locationsalong the length of a run. Such a hose has the classic problem of overwatering plants near the inlet end of the hose and under watering plantsat locations distant from this inlet end. If the value of "x" is lessthan 0.5, then the hose is considered to be pressure compensated, andthe drip-flow irrigation rate is not simply a function of applied waterpressure but is somewhat independent of the internal water pressure atparticular locations along the length of a hose run. Such an irrigationhose provides a more uniform water delivery along the length of a longrun of the hose. Ideally, if the value for "x" is zero the hose is fullypressure compensated, and the irrigating drip-flow rate would beconstant irrespective of internal water pressure. Such an idealizedirrigation hose does not exist.

SUMMARY OF THE INVENTION

In view of the deficiencies of the conventional related technology, aprimary object for this invention is to provide an irrigation tape whichavoids one or more of these deficiencies.

An additional object for this invention is to provide a drip irrigationhose which has a substantially constant rate of water delivery along itslength over a wide range of internal water pressures.

Still another object is to provide such a drip irrigation hose which hastwo discreet ranges of substantially constant drip irrigation waterdelivery, each having a corresponding range of internal water pressuresso that a user of the hose may choose to irrigate plants either in alight watering range or in a heavier watering range of the hosedependent upon which internal water pressure the user chooses to supplyto the hose.

Another object for this invention is to provide such an irrigation hosewhich has the ability to clear itself of clogging contamination upon therelief and reapplication of water pressure in the hose.

Yet another object for this invention is to provide a drip irrigationhose with water inlet features leading from the primary water flow pathto the secondary drip-flow paths which resist clogging by contaminantsin the hose.

Still further, another object for this invention is to provide a dripirrigation hose which includes turbulence enhancing features effectiveupon flushing through of the hose to scrub the inlets to the secondarydrip flow paths free of contamination and debris which may have lodgedat these inlets.

Still further, another object for the present invention is to providesuch an irrigation hose which allows the secondary drip-flow channels tobe sized as large as is practicable so that contamination which doesenter these passages will pass through without clogging the hose.

Yet another object for this invention is to provide such a dripirrigation hose which includes features closing the drip-flow outlets ofthe hose when water is not being discharged therefrom, which will openwidely enough to allow contamination to be ejected from the hose so thatthis contamination does not clog the hose at the drip-flow outlets, andyet which will resist the reflux of environmental water into the hoseand also will resist the entry of plant roots into the hose.

Accordingly, the present invention provides a drip irrigation hose ofthe type having an elongate primary water flow path extendingtherethrough and a drip-flow secondary flow path extending from theprimary flow path to open outwardly of the hose, the drip irrigationhose including a hose body with a wall circumscribing and bounding theprimary flow path, the wall including a first wall portion and a secondwall portion which are overlapped and sealingly connected to one anotherto define the secondary flow path therebetween, one of the first wallportion and the second wall portion defining a tortuouscontinuously-open channel forming a part of the secondary flow path, andthe first and the second wall portions being variably spaced from oneanother to define a variable-area part of the secondary flow path, oneof the first wall portion and the second wall portion beingpressure-responsive to move toward the other of the first wall portionand the second wall portion to constrict the variable-area part of thesecondary flow path in response to increasing water pressure within thehose.

These and additional objects and advantages for the present inventionwill be apparent from a reading of the following detailed description ofseveral exemplary embodiments of the present invention, taken inconjunction with the appended drawing figures, which are brieflydescribed below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a fragmentary perspective view of an irrigated field inwhich plural constant-flow drip irrigation tape hoses according to thepresent invention are in use to irrigate growing plants;

FIG. 2 is a fragmentary perspective view of a section of theconstant-flow drip irrigation tape hose seen in FIG. 1, with portions ofthe structure broken away and removed for clarity of illustration;

FIG. 3 provides an enlarged fragmentary view taken at arrows 3--3 ofFIG. 2, and showing in internal feature of the drip irrigation tape hoseseen in FIGS. 1 and 2;

FIG. 4 is a fragmentary cross sectional view taken at line 4--4 of FIG.3;

FIGS. 5 and 6 provide enlarged axial views of the constant-flow dripirrigation tape hose seen in FIGS. 1-4, and in two alternative operatingconditions dependent upon the internal water pressure carried by thehose;

FIG. 7 graphically represents operation of the constant-flow dripirrigation tape hose seen in FIGS. 1-6;

FIGS. 8 and 9 illustrate steps in the process of manufacturing aconstant-flow drip irrigation tape hose according to the precedingdrawing Figures;

FIGS. 10 and 11 illustrate steps in the process of making an alternativeembodiment of the present constant-flow drip irrigation tape hose, whichembodiment is functionally equivalent to the embodiment of FIGS. 1-9;

FIG. 12 provides a fragmentary perspective view similar to that of FIG.2, but illustrating an alternative embodiment of the presentconstant-flow drip irrigation tape hose;

FIGS. 13 and 14 provide fragmentary perspective views of steps in theprocess of making a drip irrigation tape hose as seen in FIG. 12;

FIG. 15 is an enlarged fragmentary cross sectional view taken at line15--15 of FIG. 14;

FIG. 16 illustrates a step in the process of making an alternativeembodiment of the present constant-flow drip irrigation tape hose, whichis similar to the embodiment seen in FIGS. 12-15;

FIGS. 17 and 18 provide respective perspective and transverse sectionalviews of another alternative embodiment of the constant-flow dripirrigation according to the present invention, which embodiment providestwo alternative constant-flow drip irrigation ranges dependent upon theinternal water pressure provided to the hose; and

FIG. 19 graphically presents the operation of the constant-flow dripirrigation tape hose seen in FIGS. 17 and 18.

DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENTS OF THEINVENTION

Viewing now FIG. 1, a field 10 is seen to include growing plants 12which are arranged in rows. A manifold pipe 14 extends across the field10 at one end thereof. This manifold pipe carries irrigation water, asis indicated by the arrows 16. Connecting with the manifold pipe 14 is aplurality of elongate constant-flow drip irrigation tape hoses 18. Thedrip irrigation tape hoses 18 extend in long runs generallyperpendicularly from the manifold pipe 14 along the length of the rowsof growing plants 12. The tape hoses 18 also carry irrigation water, asis indicated by the arrows 20. Spaced regularly along the length of eachtape hose 18 is a plurality of drip sites, indicated with the arrows 22.The drip sites 22 will ordinarily be spaced from about 6 inches to about12 inches apart. From the drip sites 22 issues a dripping flow ofirrigation water to the growing plants 12. This dripping flow of waterwill be at a selected rate of from about 0.05 gallon per hour to about1.0 gallon per hour.

Generally, the tape hoses 18 are dead-headed at their ends remote fromthe manifold pipe 14. That is, the remote ends (not seen in the drawingFigures) of the drip irrigation tape hoses 18 are simply clamped shut.Consequently, all of the water which enters a particular run of the dripirrigation tape hose 18 will be discharged therefrom via the dripirrigation sites 22 along the length of hose. During irrigation use ofthe tape hoses 18, the water flow rate in the tape hoses 18 is ratherslow, and is at a controlled pressure of about 4 to about 15 psig at theend of the runs adjacent to the manifold pipe 12. Understandably, thewater pressure within each hose 18 decreases along the length of eachrun. That is, because the tape hoses 18 may be any where from a few feetin length to a thousand feet or more in length, the flow-frictionpressure losses and volume-loss pressure losses in the tape hoses 18combine to produce a considerable difference in the internal waterpressure within each hose at its end next to the manifold pipe 14 ascompared to the water pressure at the remote dead-headed end of eachhose 18.

Also, all of the contaminating bacterial slime, algae, and particulateswhich enters a run of the tape hose 18 will be trapped therein.Ordinarily, users of such drip irrigation tape hoses occasionally willopen the clamp at the remote end of each run and allow a few minutesduring which the water can flow freely and flush through the hose toremove contamination. The effect of this flushing water flow will beexplained further hereinbelow.

Viewing now FIGS. 2-9 in conjunction, it is seen that the constant-flowdrip irrigation tape hose 18 includes an elongate hose body 24, which isformed of a single elongate strip 26 of plastic material (seen in FIGS.8 and 9). This strip of plastic material will generally be 2 inches toabout 4 inches wide, dependent upon the diameter of hose to be made, andwill be from about 0.004 to about 0.020 inches thick. A variety ofplastic polymers and copolymers are suitable for use in making the hose18. For example, a blend of high and medium density polyethylenes may beused to make the strip 26 used in the fabrication of the hose 18. Thestrip 26 is wrapped on itself and is partially overlapped and sealed toitself adjacent to opposite longitudinal side edges 28, 30 (as is seenin FIGS. 8 and 9), to form an elongate tubular body. The tape hose body24 conventionally has a pair of opposite side longitudinal creases 32(only one of which is visible in FIG. 2) so that when the hose 18 is notsubjected to internal water pressure, it collapses to a flat tapeconfiguration. As is known, this flat tape configuration for dripirrigation hoses makes them easier to ship, to transport to and fromfields, to arrange in the fields, and to roll up for removal from thefields after the growing season is ended.

Also, viewing FIG. 2, it is seen that the tape hose 18 defines alongitudinal primary water flow path 34, through which the irrigationwater 20 flows. In order to provide the drip irrigation water flows, thetape hose 18 also defines a secondary water flow path 36, which is bestseen in FIGS. 5 and 6, and which is generally indicated by the arrowedlead lines. The water flow path 36 is defined between overlapped andsealingly united opposite marginal edge sections 38, 40, of the strip26, which are best seen in FIGS. 8 and 9. These opposite marginal edgesections 38, 40 are overlapped and are sealingly attached to one anotherby longitudinal adhesive beads 42, 44, seen in FIGS. 5, 6, and 9. As isseen in FIGS. 2, 5, and 6, these overlapped opposite marginal edgesections 38 and 40, define respective inner and outer wall portions (46,48, respectively) of the secondary flow path 36.

Under operating conditions for the irrigation hose 18 in which thepressure of water flow 20 is in a first lower pressure range (as will befurther described), the wall portions 46 and 48 are spaced radiallyapart to define a longitudinal pressure-responsive variable-area flowpath 50 (as is seen in FIG. 6). The variable-area flow path 50 defines apart of the flow path 36. Also, the outer wall portion 48 defines alongitudinally-extending continuous serpentine protrusion 52 outwardlyon the hose 18. This serpentine protrusion 52 is produced by embossing alongitudinal serpentine channel 54 (best seen in FIG. 8) into the strip26 at the marginal edge section 38. Accordingly, the serpentine channel54 communicates with the variable-area flow path 50, and also defines apart of the flow path 36. As FIG. 5 shows, during operating conditionsfor the hose 18 in which the pressure of water flow 20 is at or above acertain level, the inner wall portion 46 engages the outer wall portion48 so that the variable area flow path 50 is essentially closed off.However, the serpentine channel 54 remains open so that the flow path 36remains open with a comparatively smaller cross sectional area for theflow of water. In view of the above, it is seen that the secondary flowpath 36 includes both a continuously open tortuous serpentine flow pathportion 54, and a variable-area pressure-responsive flow path portion50.

Water flow from the primary flow path 34 into the secondary flow path 36is provided by a plurality of spaced apart port structures, generallyindicated with the numeral 56, along the length of the hose 18. The portstructure 56 is provided by forming a grouped plurality of individualports 58 through the strip 26 in the marginal edge section 40, as isseen in FIGS. 2, 3, 4, 8, and 9. These ports 58 are formed bylongitudinally slitting and embossing the strip 26 to form a group ofinwardly extending oppositely-directed individual protrusions 60. Theprotrusions 60 are of a height slightly greater than the thickness ofthe strip 26 so that a small longitudinally-extending port opening 58 isprovided at each protrusion 60. As FIG. 3 shows, the ports 58 arelongitudinally extending so that the water flow 20 in the primary flowpath 34 of the hose 28 is parallel with and across the face 62 of theports 58. This disposition for the ports 58 is believed to significantlyreduce the occurrence of contaminants in the water flow 20 becominglodged in and clogging the ports 58. Also, because the protrusions 60extend into the primary flow path 60, during flushing water flowconditions the protrusions 60 each cause their own turbulence orvorticity in the rapidly flowing flushing water. Consequently, thevorticity from the protrusions 60 assists in scrubbing contaminants fromthe interior of the hose 18 in the area of the ports 58.

Similarly, dripping water flow from the secondary flow path 36 outwardlyof the hose 18 (i.e., at the dripping sites 22) is provided by aplurality of spaced apart V-shaped outlet ports 64 formed in themarginal edge section 38 of the strip 26 (viewing FIG. 8 especially) bycorresponding V-shaped slits. The outlet ports 64 include a flap portion66 which is flexibly attached to the strip 26 between the sides of theV-shaped slits which define the ports 64. These flap portions 66 arenormally disposed generally in the plane of the strip 26 and close theport 64. However, the flow of irrigating water from within the hose 18outwardly of the ports 64 is effective to lift the flaps 66 sufficientlyto allow this flow (viewing FIGS. 2, 5, 6, and 9). Also, the ports 64are of sufficient size to pass any contamination which reaches this portvia the flow path 36. Flaps 66 are sufficiently compliant to allowcontamination which does reach the ports 64 via the-secondary flow path36 to be ejected by the dripping water flow.

On the other hand, when water is not flowing outwardly via the ports 64,the flaps 66 close these ports so that environmental water does notreflux into the hose 18. Additionally, the flaps 66 at ports 64 aresufficient to discourage small plant roots from growing into the hose18. It will be understood that the ports 56 between the primary flowpath 34 and the secondary flow path 36 alternate along the length of thehose 18 with the outlet ports 64. Consequently, water flow into the flowpath 36 via the ports 58 may flow in either direction along the lengthof the hose 18, as is indicated by the arrows on FIGS. 3 and 9.

Further consideration now of FIGS. 5 and 6 along with FIG. 7 will revealthat the combination secondary flow path 36 of the present dripirrigation tape hose 18 provides an operating range of internal waterpressures for the hose within which the rate of dripping water flow fromthe hose is nearly constant. In other words, near the manifold pipe 14,the pressure of the flowing water 20 will be the highest. As isindicated in FIG. 5, under these pressure conditions, the wall portion46 is forced by internal water pressure in the primary flow pathoutwardly into engagement with the outer wall portion 48. Consequently,the flow path 36 includes only the constant-area section provided by thetortuous serpentine channel 54, which is turbulent in flowcharacteristic. As FIG. 7 shows, the serpentine channel 54 would providea water flow from the outlet port 64 represented by the line 68.

However, at a distance from the manifold pipe along a run of the hose18, the water pressure will be lower, and the inner wall 46 will bespaced from the outer wall 48 (as seen in FIG. 6) because of theresilience and elasticity of the material from which the hose 18 isfabricated. Under these pressure conditions, the secondary flow path 36includes the variable area portion 50, providing a turbulent flowcharacteristic due to the labyrinthine passage caused by the serpentineembossments forming the channel 54. That is, the flowing water in theportion 50 of the secondary flow path flows longitudinally of the tapehose 18, crossing repeated ridges and valleys formed by the switchbacksin the serpentine channel 54. FIG. 7 shows with a line 70 the drippingwater flow from the outlet ports 64 which would be provided by thevariable-area portion 50 along. A line 72 on FIG. 7 shows the total ofthe water flows from outlet ports 64 which is provided by thecombination of the constant area flow channel 54 and variable-area flowportion 50 of the flow path 36. As is seen on FIG. 7, within a pressurerange indicated with the numeral 74, the hose 18 provides a nearlyconstant dripping water flow rate from the dripping sites 22 regardlessof the pressure of the internal water flow 20 within the hose 18.Consequently, over an extended length of the hose 18, the irrigatedplants 12 receive substantially the same amount of irrigation waterdespite the pressure drop within the hose 18 with increasing distancefrom the manifold pipe 14. Within the pressure range indicated with thenumeral 74, the present drip irrigation hose approaches the x=0 value ofthe idealized irrigation hose discussed above.

An additional advantage of the present drip irrigation hose 18 becomesapparent when one considered what happens at the secondary flow path 36when the water flow 20 is turned off, and is then turned back on again.This off/on sequence for the water flow 20 may occur when the end of oneday of irrigation is followed by the start of the next day, for example.When the water flow 20 is turned off and pressure within the hose 18 isrelieved, the secondary flow path 36 expands toward its condition seenin FIG. 6. Consequently, any contamination which has enteredthis-secondary flow path is loosened. When the water flow and pressureare turned back on, the loosened contamination will be flushed from thesecondary flow path 36 and out the outlet port 64.

FIGS. 8 and 9 illustrate steps in the making of hose 18 from strip 26.As is seen, the strip 26 is longitudinally embossed to provide theserpentine protrusion 52 and opposite serpentine channel 54. Similarly,longitudinal embossing of the strip 26 provides the protrusions 60, withadjacent slitting providing the ports 58. However, the strip 26 is alsolongitudinally embossed to provide longitudinal grooves 76-82. As isseen in FIG. 9, the grooves 76 and 80 cooperate with one another toprovide a longitudinal space for the adhesive bead 44. Grooves 78 and 82similarly cooperate with one another to provide space for adhesive bead42. FIG. 9 illustrates the condition of the strip 26 after the adhesivebeads 42 and 44 have been applied and preparatory to completion of theoverlapping of the marginal edge sections 38, 40, and sealing of thesesections to one another.

FIGS. 3 and 8 also illustrate another feature of the present dripirrigation hose 18 which is important when the hose is flushed out asdescribed above. During such flushing of the hose, the water flow 20therethrough is much faster and more vigorous than is the case duringirrigating use of the hose 18. Consequently, the disposition of theports 58 allows a vigorous water flow across the faces 62 so thancontamination is swept away. In order to improve further the scrubbingaction of the high speed vigorous water flow at the ports 58, the strip26 is embossed with a vortex-shedding structure 84 longitudinally spacedupstream slightly from and axially aligned with each end port structure56. As is seen in FIGS. 3 and 8, this vortex shedding structure 84 maytake the form of a cylindrical inwardly extending protrusion formed inthe inner wall portion 46. During flushing of the hose 18, the waterflow will be sufficiently vigorous that the structure 84 will shed aseries of vortices, which will sweep downstream and across the ports 58.These vortices will form a vortex street from each lateral side of theprotrusion 84, which vortex street is indicated on FIG. 3 with thenumeral 84'. The vortices of the vortex streets 84' pass downstreamalong the ports 58 and will help scrub away contamination accumulated inthe area of the port structure 56. Two structures 84 are provided, oneat each end of the port structure 56 because the hose 18 may be usedwith water flow in either direction.

FIGS. 10 and 11 illustrate steps in the making of another embodiment ofthe drip irrigation hose according to the present invention. The hoseembodiment made as illustrated in FIGS. 10 and 11 is functionallyequivalent to the hose of FIGS. 1-9, but has a smooth outer wall (i.e.,without an outwardly visible serpentine protrusion 52 as is seen in FIG.2). In order to obtain reference numerals for use in describing theembodiment of FIGS. 10 and 11, features of these Figures which areanalogous in structure or function to features described above arereferenced with the same numeral used above and having one-hundred (100)added thereto. The embodiment of constant-flow drip irrigation hoseshown in FIGS. 10 and 11 is formed from an elongate strip 126 ofmaterial with the marginal edge section 138 having only the longitudinalgrooves 176 and 178, and spaced apart outlet ports 164. The othermarginal edge section 140 includes an inwardly extending serpentineprotrusion 152, which provides an outwardly disposed serpentine channel154. Alternating along the length of the strip 126 with the outlet ports164, are the port structures 156. In this case, the plural ports 158 ofthe port structures 156 are spaced sufficiently apart and are relativelypositioned with the serpentine channel 154 so that the ports 158 aredisposed atop the backbends of the serpentine channel 154.

The marginal edge sections 138 and 140 are overlapped and sealinglyattached to one another so that the substantially smooth section 138 isthe outer one of these marginal edge sections, as is seen in FIG. 11. Anadvantage of the embodiment seen in FIGS. 10 and 11 is that the entirecircumferential outer wall of the irrigation hose 118 is substantiallysmooth. Accordingly, hoop stresses created in the hose by internal waterpressure are carried by a wall structure which is substantially free ofstress concentrators (except for the outlet ports 164). Thus, theembodiment of FIGS. 10 and 11 is better suited for irrigation uses inwhich the pressure of the irrigation water will be rather high.

FIGS. 12-15 illustrate yet another alternative embodiment of the presentconstant-flow drip irrigation tape hose in which the outer surface ofthe hose is substantially smooth, and is without a longitudinallyextending serpentine protrusion as was seen in the embodiment of FIGS.1-9. In order to obtain reference numerals for use in describing theembodiment of FIGS. 12-15, features of this embodiment which are thesame as or which are functionally analogous to features depicted anddescribed in a preceding Figure are referenced with the same numeralused above and increased by two-hundred (200).

Viewing FIG. 12 an irrigation hose 218 is seen which includes plurallongitudinally spaced and sealingly separate drip flow-ratewater-metering secondary flow paths 236. The longitudinally extendingserpentine protrusion 252 and serpentine channel 254 of this embodimentare not longitudinally continuous. Viewing FIG. 13, it is seen that themarginal edge sections 238 and 240 each include respective longitudinalgrooves 276-282, similarly to the hoses described above. These grooves176-282 likewise receive beads of adhesive to sealingly bond the edgesections 238 and 240 to one another in overlapping relation. However,the marginal edge sections 238 and 240 also include longitudinallyspaced apart matching transverse grooves 86 and 88. These grooves 86 and88 also receive a transverse bead 90 of adhesive (best seen in FIG. 14).The adhesive beads 90 sealingly separate adjacent secondary flow paths236 into discreet longitudinal drip flow-rate metering sections.

At one end, these discreet drip flow-rate metering sections 236 includea respective port structure 256, similar to that described above withreference to FIGS. 10 and 11. At the opposite end of each discreetmetering section, the marginal edge section 238 defines an outlet port264. However, this outlet port 264 is defined by a star burst cutthrough the strip 226. That is, the outlet port 264 includes a pluralityof V-shaped flaps 266 (as are seen in FIG. 13. The flaps 264cooperatively close the outlet port 264, but will open sufficientlywidely to allow contamination to pass outwardly through this port.Congruent with the outlet port 264 is a basin termination portion 92 ofthe serpentine channel 254. That is, the serpentine channel 254communicates into the basin portion 92.

Also congruent with the outlet port 264 and centered under the flaps 266is a flat-topped island 94 in the basin 92. This island 94 is formed bya reentrant of the embossed groove which forms the serpentine channel254 and basin 92. As is shown by FIG. 15, this flat-topped islandfeature 94 in basin 92 is effective to inwardly support the plural flaps266 of the outlet port 264 when these flaps are not being opened byoutward water flow. Consequently, the outlet port 264 is effectivelysealed with respect to reflux into the hose 218 of environmental water,and plant roots are also prevented from entering the secondary flow path236.

An advantage of the embodiment of the present invention shown in FIGS.12-15 is that because each outlet port is fed irrigation water by asingle length of serpentine channel 254 and by a single port structure256, the sizes of these features may be made as large as is practicablein view of the desired drip metering rate of a particular hose.Consequently, the hose of FIGS. 12-15 will be particularly resistant toclogging by contamination in the irrigation water. For example, theserpentine channel 254 may be made twice as large in cross sectionalflow area, or larger, than the channel 54 illustrated in FIGS. 1-9, fora particular rate of drip flow from the hose 218.

FIG. 16 illustrates another alternative embodiment of the presentinvention. In order to obtain reference numerals for use in describingthis embodiment of the invention, the familiar numerals are againincreased by one-hundred (by 300 with respect to the numerals used onFIGS. 1-9). The drawing Figure illustrates a strip 326 which is similarto strip 226 described above. However, rather than sealingly separateadjacent drip flow-rate water-metering secondary flow paths 336, theseadjacent flow paths are simply separated by a labyrinth said feature 96.The use of a labyrinth seal feature eliminates the need to apply thetransverse adhesive beads 90. The labyrinth seal feature 96 is formed byplural transverse embossed protrusions 98, which form correspondingalternating lands and grooves (not seen in the drawing Figures) inwardlyof the secondary flow path 336. The labyrinth seal structure 96 iseffective to insure unidirectional flow of metering water in thediscreet secondary flow paths 236. Accordingly, the advantage of beingable to form the inlet port structure 356, serpentine 354, and outletport 364 all as large as is practicable in view of the desired drippingwater outflow rate so that clogging of the hose is reduced.

Yet another alternative embodiment of the present invention isillustrated by FIGS. 17 and 18, with the water flow characteristic ofthis hose as a function of applied water pressure being presented inFIG. 19. Reference numerals for use in describing familiar features ofthis embodiment are increased by 400 with respect to the numeral used toreference the same or analogous features of the first embodiment of theinvention. FIGS. 17 and 18 show a drip irrigation hose 418 with anoutwardly exposed longitudinally continuous serpentine protrusion,similarly to the hose of FIGS. 1-9. This hose includes port structures456 and outlets 464 (not seen in the drawing Figures) like theembodiment of FIGS. 1-9. However, the embodiment of FIGS. 17 and 18 alsoincludes a longitudinally continuous embossed protrusion 100, providinga corresponding longitudinally continuous groove 102 inwardly of thesecondary flow path 436. Because of the groove 102, the serpentinechannel 454 is not of constant area along its tortuous length, but isconstantly open as will be seen.

As is illustrated by the solid-line, dash-and-dot line, and dashed-linealternative positions for the inner wall portion 446 in FIG. 18, thiswall may occupy a low pressure position (dashed-and-dot lines in FIG.18, and as seen in FIG. 17), an intermediate pressure position (solidlines), or a high pressure position (dashed lines). Consequently, whenthe irrigation hose is provided with low pressure water, thevariable-area portion 450 of the secondary flow path 436 will have awidth as seen in FIG. 17, and as indicated by the reference numeral 104in FIG. 18. At an intermediate pressure level, the inner wall portion446 will engage the outer wall portion 448 so that the secondary flowpath is reduced in area and has a width indicated by the numeral 106 inFIG. 18. An additional increase in water pressure will result in theinner wall portion 446 conforming more closely to the shape of the outerwall portion 448 so that the elongate groove 102 is also closed by theinner wall portion 446. Consequently, the secondary flow path 436thereafter has a minimum area as is seen in FIG. 18 referenced with thenumeral 454. This serpentine channel 454 does not have a constant crosssectional flow area along its tortuous length, but has a series of areaminima as seen in FIG. 18.

FIG. 19 graphically illustrates the resulting water flow characteristicsfor the hose 418 seen in FIGS. 17 and 18. As can be seen, a line 468represents the water output which would be provided by the serpentinechannel 454 alone. A line 470 represents the water output which would beprovided by the portion of variable area flow path 450 exclusive of thearea of longitudinal groove 102. Another line 470' represents the waterflow rate which would be provided by the portion of the variable-areaflow path 450 defined by groove 102 alone. By addition of theseindividual water flow rates, the line 472 represents the total waterdrip output flow rate provided by the hose 418. As can be easily seen,the hose 418 provides a low-pressure range (474'), and a high pressurerange (474"), within which the water drip output rate of the hose issubstantially uniform despite a considerable difference in waterpressure level within the hose. The result is that the hose 418 allows auser to irrigate row plants at either one of two watering ratesdependent upon the water pressure level which the user supplies to theinlet end of a run of the hose. Within either of the constant-flowpressure ranges of the hose 418, the plants along a considerable lengthof the hose will receive substantially the same amount of water. Thatis, within the two water pressure ranges indicated, the irrigating hoseof this embodiment approaches the x=0 value of an idealized irrigationhose.

While the present invention has been depicted, described, and is definedby reference to particularly preferred embodiments of the invention,such reference does not imply a limitation on the invention, and no suchlimitation is to be inferred. The invention is capable of considerablemodification, alteration, and equivalents in form and function, as willoccur to those ordinarily skilled in the pertinent arts. For example, itis apparent that the sealing lines of the present embodiments may beeffected in a variety of ways other than the use of adhesive beads asdisclosed. These sealing lines could be effected by using ultrasonic orthermal welding of the plastic material of the hose wall to itself, forexample. Thus, the depicted and described preferred embodiments of theinvention are exemplary only, and are not exhaustive of the scope of theinvention. Consequently, the invention is intended to be limited only bythe spirit and scope of the appended claims, giving full cognizance toequivalents in all respects.

We claim:
 1. A constant-flow drip irrigation hose of the type having anelongate primary water flow path extending therethrough and a secondaryflow path extending from said primary flow path to open outwardly ofsaid hose, said drip irrigation hose comprising;a hose body with a wallcircumscribing and bounding said primary flow path, said wall includinga first wall portion and a second wall portion which arecircumferentially overlapped and sealingly connected to one another todefine said secondary flow path therebetween, one of said first wallportion and said second wall portion defining a tortuouscontinuously-open channel forming a first part of said secondary flowpath, and said first and said second wall portions being variably spacedfrom one another to define a variable-area second part of said secondaryflow path, one of said first wall portion and said second wall portionbeing pressure-responsive to move toward the other of said first wallportion and said second wall portion to constrict said variable-areasecond part of said secondary flow path in response to increasing waterpressure within said hose; with one of said first wall portion and saidsecond wall portion additionally defining a longitudinally-extendinggroove defining a third variable-area part of said secondary flow path,and one of said first wall portion and said second wall portion beingfurther pressure-responsive and movable toward the other of said firstwall portion and said second wall portion to constrict saidvariable-area third part of said secondary flow path in response toincreasing water pressure within said hose after said variable areasecond part of said secondary flow path has been substantially closed.2. The drip irrigation hose of claim 1 wherein said tortuouscontinuously-open channel is of serpentine configuration.
 3. The dripirrigation hose of claim 2 wherein said continuously open serpentinechannel communicates at one end thereof with a basin, said basin beingaligned with an outlet port of said hose which is defined by the otherone of said first wall portion and said second wall portion.
 4. The dripirrigation hose of claim 1 wherein said first wall portion and saidsecond wall portion are sealingly connected to one another atcircumferentially spaced apart longitudinal sealing lines disposed onopposite sides of said secondary flow path.
 5. The drip irrigation hoseof claim 4 wherein said first wall portion and said second wall portionare additionally sealingly interrelated to one another at longitudinallyspaced apart circumferential labyrinth lines to inhibit secondary waterflow between longitudinally adjacent sections of said secondary flowpath.
 6. The drip irrigation hose of claim 4 wherein saidcircumferentially spaced apart longitudinal sealing lines are defined bymatching longitudinal grooves in said wall, and a bead of adhesivematerial received in said grooves.
 7. The drip irrigation hose of claim4 wherein said first wall portion and said second wall portion areadditionally sealingly connected to one another at longitudinally spacedapart circumferential sealing lines to sealingly separate longitudinallyadjacent sections of said secondary flow path from one another.
 8. Thedrip irrigation hose of claim 1 wherein said wall further defines a portstructure communicating water flow from said primary flow path to saidsecondary flow path, said port structure including a plurality of slitsalong the one of said first wall portion and said wall portion boundingsaid primary flow path.
 9. The drip irrigation hose of claim 8 whereinsaid port structure includes a protrusion extending inwardly of saidprimary flow path from the inner one of said first wall portion and saidsecond wall portion, a longitudinal slit through said inner one of saidwall portions adjacent to said protrusion, and said inner one of saidwall portions being displaced inwardly at said protrusion a distancegreater than the thickness of said one wall portion to opencommunication from said primary flow path to said secondary flow path.10. The drip irrigation hose of claim 9 wherein said port structureincludes a plurality of substantially identical protrusions andassociated longitudinal slits opening communication between said primaryflow path and said secondary flow path, said plurality of slits andprotrusions being spaced longitudinally along said inner wall portion.11. The drip irrigation hose of claim 10 wherein said plurality ofsubstantially identical protrusions and associated longitudinal slitsare alternately disposed in circumferentially opposite directionslongitudinally along said inner wall.
 12. The drip irrigation hose ofclaim 11 wherein said plurality of substantially identical protrusionsand associated longitudinal slits are disposed in a staggered arraylongitudinally along said inner wall.
 13. The drip irrigation hose ofclaim 9 wherein said tortuous continuously-open channel is of serpentineconfiguration and is defined by an inner one of said first wall portionand said second wall portion, said port structure including a pluralityof substantially identical protrusions and associated longitudinal slitsopening communication between said primary flow path and said secondaryflow path, said plurality of slits and protrusions being spacedlongitudinally along said inner wall portion, and said plurality ofsubstantially identical protrusions and associated longitudinal slitsalso being alternately disposed in circumferentially opposite directionslongitudinally along said inner wall so that said plurality ofsubstantially identical protrusions and associated longitudinal slitsare disposed in a staggered array longitudinally along said inner walland are disposed atop said backbends of said serpentine channel.
 14. Thedrip irrigation hose of claim 8 further including a vortex sheddingstructure disposed immediately upstream of and spaced from said slits ofsaid port structure for shedding flow vortices during flushing of waterthrough said hose, whereby said vortices shed from said structure sweepdownstream in the flushing water flow forming a vortex street scrubbingacross said port structure to remove contamination therefrom.
 15. Thedrip irrigation hose of claim 14 including a pair of said structures forshedding vortices arranged one on each side of said port structure toallow bi-directional flushing water flow through said hose withattendant vortex scrubbing of said port structure irrespective of thedirection in which the flushing water flows.
 16. The drip irrigationhose of claim 14 wherein said vortex shedding structure includes theinner one of said first wall portion and said second wall portiondefining a bluff cylindrical protrusion extending inwardly of said innerwall immediately upstream of said port structure.
 17. The dripirrigation hose of claim 8 wherein said port structure includes aprotrusion extending inwardly of said primary flow path from the innerone of said first wall portion and said second wall portion, said innerone of said first wall portion and said second wall portion defining anopening on said protrusion extending through said inner one of said wallportions to communicate with said secondary flow path, whereby saidprotrusion generates vortices during flushing water flow through saidprimary flow path to scrub contamination from said port structure. 18.The drip irrigation hose of claim 1 wherein said wall further defines anoutlet port structure communicating water flow from said secondary flowpath outwardly of said hose.
 19. The drip irrigation hose of claim 18wherein said outlet port structure includes an outer one of said firstwall portion and said second wall portion defining at least a pair ofslits intersecting to define both said outlet port and an integralshape-matching flap portion of said outer wall yieldably closing saidoutlet port, said flap portion yielding in response to water flowoutwardly of said secondary flow path to permit said water flow toescape from said hose.
 20. The drip irrigation hose of claim 19 whereinsaid outlet port structure includes an inner one of said first wallportion and said second wall portion defining a surface portionunderlying said flap portion of said outer wall and resisting inwardmovement of said flap portion.
 21. The drip irrigation hose of claim 20wherein said surface portion underlying said flap portion is defined bya protrusion of said the inner one of said first wall portion and saidsecond wall portion, said protrusion having a substantially flat outerend supportingly engaging said flap portion.
 22. The drip irrigationhose of claim 1 wherein said additional longitudinally-extending grooveis partially overlaid by said tortuous continuously-open channel.
 23. Adrip irrigation hose of the type having an elongate primary water flowpath extending therethrough and a secondary flow path extending fromsaid primary flow path to open outwardly of said hose, said dripirrigation hose comprising:a hose body with a wall circumscribing andbounding said primary flow path, said wall including a wall portiondefining said secondary flow path therein, said wall further defining aport structure communicating water flow from said primary flow path tosaid secondary flow path, and said port structure includes a protrusionextending inwardly of said primary flow path from said wall, said walldefining an opening on said protrusion extending through said wall tocommunicate with said secondary flow path, whereby said protrusiongenerates vortices during flushing water flow through said primary flowpath to scrub contamination from said port structure.
 24. The dripirrigation hose of claim 23 wherein said port structure includes alongitudinal slit through said wall on said protrusion, and said wallbeing displaced inwardly at one side of said slit a distance greaterthan the thickness of said wall to open communication from said primaryflow path to said secondary flow path.
 25. The drip irrigation hose ofclaim 24 wherein said port structure includes a plurality ofsubstantially identical protrusions and associated longitudinal slitsopening communication between said primary flow path and said secondaryflow path, said plurality of slits and protrusions being spacedlongitudinally along said wall.
 26. A drip irrigation hose of the typehaving an elongate primary water flow path extending therethrough and asecondary flow path extending from said primary flow path to openoutwardly of said hose, said drip irrigation hose comprising:a hose bodywith a wall circumscribing and bounding said primary flow path, saidwall including a wall portion defining said secondary flow path therein,said wall further defining a port structure communicating water flowfrom said primary flow path to said secondary flow path, andvortex-shedding structure means disposed immediately upstream of saidport structure for shedding flow vortices during flushing of waterthrough said hose, whereby vortices shed from said structure means sweepdownstream in the flushing water flow forming a vortex street scrubbingacross said port structure to remove contamination therefrom.
 27. Thedrip irrigation hose of claim 26 including a pair of saidvortex-shedding structure means for shedding vortices, said pair ofstructure means being arranged one on each side of said port structureto allow bi-directional flushing water flow through said hose withattendant vortex scrubbing of said port structure irrespective of thedirection in which the flushing water flows.
 28. The drip irrigationhose of claim 26 wherein said vortex-shedding structure means includessaid wall defining a bluff cylindrical protrusion extending inwardly ofsaid wall immediately upstream of said port structure.
 29. Aconstant-flow drip irrigation hose of the type having an elongateprimary water flow path extending therethrough and a secondary flow pathextending from said primary flow path to open outwardly of said hose,said drip irrigation hose comprising;a hose body with a wallcircumscribing and bounding said primary flow path, said wall includinga first wall portion and a second wall portion which arecircumferentially overlapped and sealingly connected to one another todefine said secondary flow path therebetween, one of said first wallportion and said second wall portion defining a tortuouscontinuously-open channel forming a first part of said secondary flowpath, and said first and said second wall portions being variably-spacedfrom one another to define a variable-area second part of said secondaryflow path, one of said first wall portion and said second wall portionbeing pressure-responsive to move toward the other of said first wallportion and said second wall portion to constrict said variable-areasecond part of said secondary flow path in response to increasing waterpressure within said hose; said wall further defining a port structurecommunicating water flow from said primary flow path to said secondaryflow path, said port structure including a protrusion extending inwardlyof said primary flow path from the inner one of said first wall portionand said second wall portion, said inner one of said first wall portionand said second wall portion defining an opening on said protrusionextending through said inner one of said wall portions to communicatewith said secondary flow path, whereby said protrusion generatesvortices during flushing water flow through said primary flow path toscrumb contaimination from said port structure.
 30. A constant-flow dripirrigation hose of the type having an elongate primary water flow pathextending therethrough and a secondary flow path extending from saidprimary flow path to open outwardly of said hose, said drip irrigationhose comprising;a hose body with a wall circumscribing and bounding saidprimary flow path, said wall including a first wall portion and a secondwall portion which are circumferentially overlapped and sealinglyconnected to one another to define said secondary flow paththerebetween, one of said first wall portion and said second wallportion defining a tortuous continuously-open channel forming a firstpart of said secondary flow path, and said first and said second wallportions being variably spaced from one another to define avariable-area second part of said secondary flow path, one of said firstwall portion and said second wall portion being pressure-responsive tomove toward the other of said first wall portion and said second wallportion to constrict said variable-area second part of said secondaryflow path in response to increasing water pressure within said hose;said wall further defining a port structure communicating water flowfrom said primary flow path to said secondary flow path, said portstructure including a protrusion extending inwardly of said primary flowpath from the inner one of said first wall portion and said second wallportion, a longitudinal slit through said inner one of said wallportions adjacent to said protrusion, and said inner one of said wallportions being displaced inwardly at said protrusion a distance greaterthan the thickness of said one wall portion to open communication fromsaid primary flow path to said secondary flow path.